Radio signaling system



Feb. 11, 1930. c GQQDRUM 1,746,829

RADIO SIGNALING SYSTEM Filed July 14. 1925 /6 V M, g 49%? 1e I M135 T M;g wig? 1e: N M 7 Q hren/ar:

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Patented Feb. 11, 1930 UNITED STATES PATENT err-nos CHARLES L. GOODRUM,OF NEW YORK, N. Y., ASSIGNOR TO VES'IERN ELECTRIC COM- IPANY,INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK RADIOSIGNALING SYSTEM Application filed July 14, 1925. Serial No. 43,469.

This invention relates to signaling systems and more particularly to amethod and means for eliminating interference due to atmospheric andother disturbances in a radio signaling system.

A si nal wave transmitted from a radio sending station is frequentlydistorted due to undesired disturbances of atmospheric or other originin the transmission medium. These disturbances affect the signal wave insuch manner that upon demodulation at a distant radio receiving stationnoise currents are produced and converted into sound waves. The ratio ofthe amplitude of the undesired sound Waves to the received signals,

frequently called the noise ratio, is at times, suiilciently great toeffectively mask the received signal. This is particularly true when thereceived signal is of comparatively low intensity as the noise ratio inthat case may be very large.

It is an object of this invention to minimize the eifect of undesireddisturbances upon a signal carrying wave.

Another object is to enable signal waves received from a distant stationto be demodulated in a radio translating apparatus to re produce signalswhich are substantially free from distortion due to extraneousdisturbances.

These objects and others which will be ap parent as the nature of theinvention is disclosed are accomplished by radiating in addition to asignal carrying wave, an auxiliary carrier wave of frequency differentfrom that of the signal wave. The two waves, which will undergosubstantially identical distortion or modulation due to atmospheric andother disturbances, are combined in-the receiving apparatus in such amanner that the low frequency currents due to the disturbances opposeeach other so that they do not affect the signal responsive means, whilethe desired signal is translated and is used to actuate the signalresponsive means.

Although the novel features which are b lieved to be characteristic ofthis invention will be pointed out with particularity in the followingclaims, the invention itself, its objects and advantages, the mode ofits operation and the manner of its organization will be betterunderstood by referring to the following description taken in connectionwith the accompanying drawing forming a part thereof in which:

Fig. 1 is a diagrammatic representation of a radio signaling systemembodying this invention.

Figs. 2 and 3 show different modifications of the system illustrated inFig. 1.

Referring more particularly to Fig. 1, the transmitter T, which mayconsist of any clesired form or type of apparatus for transmitting asignal modulated carrier wave, is coupled to antenna circuit 1 by meansof transformer 2. As the particular form of transmitting apparatus isnot material to this invention, it has been shown in a conventionalmanner. A source 3 of carrier frequency oscillations differing infrequency from the wave radiated from antenna 1, is coupled by means oftransformer 5 to an antenna circuit 4 which is resonant to waves of thisparticular frequency.

Waves transmitted from antennae 1 and 4 are received by antenna 6located at a distant receiving station. Waves incident upon the antennacircuit6 are transferred to a suitable receiving apparatus R includingmeans selective of the signal frequency. The receiver R may consist ofany desired system for demodulating the signal wave received from thedistant transmitting station. Currents of the auxiliary carrierfrequency radiated from antenna 4 are transferred in the receivingstation to a receiver R which is substantially identical with thereceiver R except that it includes means for selecting the auxiliaryWave. The gain in receiver R is adjusted by potentiometers 21 to producenoise current of the desired intensity.

Audio frequency currents resulting from detection in receivers R and Rafter passing through transformers 7 and 8 respectively are impressedupon the respective input circuits of the space discharge amplifiers 9and 10. The output circuits of amplifiers 9 and 10 are connected bymeans of transformer 11 to the signal responsive device 12, so that theeffects of noise currents are mutually opposed.

In the operation of this system any modulation which occurs effectswaves from antennae 1 and 4 in substantially the same manner. The tworeceivers R and R at the receiving' station will detect these undesiredmodulations to produce the noise currents which are supplied to theprimary of the transformer 11 in. such manner that their effects uponthe receiver 12 are equal and opposite. The intensity of the noisecurrents produced by receiver R is adjusted by potentiometer 21 tosubstantially neutralize that produced by receiver R and hence thereWill be no resultant effect produced in signal indicating means 12 dueto these currents.

Since no energy due to the signal frequency wave is supplied to thereceiver R the desired signal current will be reproduced in the receiverR and will produce a response in device 12.

In systems operating in the manner described above, atmosphericdisturbances which were of sufficient intensity to efiective- 1y mask areceived signal, in systems which did not include noise, currentneutralizing means, were reduced to such an amount that the reception ofthe desired signal was not interfered with.

It has been found that the auxiliary carrier may be supplied from atransmitting antenna located at a point nearer to the receiving antennathan the signal transmitting apparatus. In this case, the auxiliarycarrier and signal modulated carrier are affected equally by undesireddisturbances which may then be balanced out and eliminated in accordancewith this invention.

In the system shown in Fig. 2 elements corresponding to those shown inFig. 1 are rep resented by correspondingly numbered parts. The source ofauxiliary oscillations 3 is coupled directly to the receiving antennacircuit 6 instead of being located at the distant point as indicated inFig. 1. With a system of this type any modulation which is effected inthe antenna circuit due to the disturbances acting upon the receivingaerial effect the auxiliary car 'ier to the same extent as the signalcarrying wave is affected in the transmitting medium and the localreceiving circuit will operate to produce effects which are balanced outor neutralized in a manner similar to that described in connection withthe operation of In the transmitter of the system shown in Fig. 3, twomodulators M and M are supplied with currents of different carrierfrequency from sources 13 and let respectively. Signal frequencycurrents from source 15 controlled by microphones 16 are impresseddirectly upon modulator M and are impressed upon modulator M throughtransformer 17. The modulated carrier currents from modulators M and Mare transferred to antenna circuits 1 and 4; respectively throughtransformers 2 and 5 as described in connection with Fig. 1. As thecurrent in the secondary of a transformer is opposite in phase to thatin the primary, transformer 17 serves as a phase changing device withthe result that signal currents impressed upon modulators M and M are180 out of phase.

In the receiving apparatus, waves of the frequency radiated by antenna 1are received by antenna 18, resonant thereto, and supplied to thereceiving set R and waves of the frequency radiated by antenna 1 arereceived by antenna '19, which is resonant to waves of this frequency,and supplied to the receiver R The two waves after being demodulated inreceivers R and R are again reversed in relative phases, i. e. 180, bytransformer 20 and used to operate a signal responsive device 12. Themodulating components of the carriers received in apparatus R and Rbeing 180 out of phase as above described, will be superimposed insignal responsive device 12 in the same phase and mutually aid inproducing the desired signal. Any extraneous modulation of the twocarriers will occur in the same phase and produce low frequency noisecurrents in the same phase in receivers 1- and R These will be impressedin mutually opposing relationship upon signal responsive device 12 andconsequently neutralize each other in the manner described in connectionwith Figs. 1 and 2.

The system shown in Fig. 3 is especially adapted to long distances pointto point signaling systems as the power may be divided between the twocarriers, in which case both carriers would aid in transmitting thesignal. In a system of this kind, the power necessary to supply theauxiliary carrier is advantageously utilized in transmitting the signaland is not, as is the case of the systems of Figs. 1 and 2, used merelyfor interference elimination.

The system of Figs. 1 and 2 is advantageous under certain conditionssuch as for relatively short distance transmission where the expense ofduplicating the modulating apparatus is not warranted A separateoscillator may be cheaply installed either at an already existingtransmitting station or in the proximity of the receiving station andgood results secured, although the power is not as efliciently utilizedas in the system of Fig. 3.

Although this invention has been disclosed as applied to particularsystems, it is not to be limited thereto but only in accordance with thescope of the invention as defined by the following claims. Obviously,radio frequency and audio frequency amplification may be used, ifdesired.

hat is claimed is:

1. The method of eliminating undesired disturbances in a carriertelephone transmitting and receiving system having a plurality of pathswhich comprises, transmitting the signals as modulations of a signalcarrier wave, receiving and clemodulating the signal carrier wave in onepath of the receiving system to produce the signal and disturbingcurrents, simultaneously supplying to a second path of the receivingsystem an auxiliary carrier wave which is aflected only by the undesireddisturbances, demodulating the auxiliary carrier wave whereby thedisturbing current alone is produced and applying the demodulationproducts in the second path to the first path to neutralize thedisturbing current produced therein whereby the signal, free fromdisturbance, is reproduced.

2. A method of eliminating undesired disturbances in a carrier telephonetransmitting and receiving system which comprises, transmitting signalsas modulations of a signal carrier wave, simultaneously supplying anauxiliary carrier wave to the receiving apparatus independently ofthesignal modulated carrier wave and in such a manner that the auxiliarywave is affected only by extraneous interfering disturbances similarlyto the signal modulated carrier wave, demodulating said wavesindependently whereby, in the one case, signal and interfering currentsdue to extraneous disturbances are produced and, in the other case, onlyinterfering currents are produced, and combining the products ofdemodulation in such manner that the interfering currents areneutralized and the signal, free from interference, is reproduced.

3. A carrier telephone signaling system comprising means for receiving asignal wave, means for demodulating said Wave, means at said receivingstation for supplying to said signal wave receiving means, an auxiliarywave unmodulated by signals, a separate means for demodulating saidauxiliary wave, and means for combining the separately produceddemodulation products to effect neutralization of similar variationspresent in the two waves.

4:. In a carrier telephone signaling system, means for transmitting asignal carrier wave, a receiving station, means at said receivingstation for supplying an auxiliary wave, unmodulated by signals, twodemodulating paths at said receiving station, one for said signalcarrier wave and one for said auxiiiary wave, and means for combiningthe demodulation products of said paths to effect neutralization ofcertain components which are present in both demodulation products.

In witness whereof, I hereunto subscribe my name this 1st day of July A.D. 1925.

CHARLES L. GOODRUM.

